WordPress Lesson 1: Remember that Auto Maintenance is NOT Auto Maintenance. My Real Estate Blog https://www.realestateauction.co.za showed a blank admin page after Auto Update. The following worked for me:
Delete all unused themes
Delete all unused Plugins
Go to Plugins page
Select all plugins
De-Activate all plugs
Activate them one by one starting with the most important plugins first
As you go down your list you might find a plugin that results in a blank admin page. Go FTP and rename the folder of the offending plugin. Back to WP and F5 – Admin will fire up again. You will have to do some code hunting to find the conflict.
Good Luck